The invention of the present application is generally directed to improved processes for affecting the preparation of seamless substrates, and more specifically, the present invention relates to powder coating processes for permitting the fabrication of flexible seamless substrates useful, for example, in the preparation of layered photoconductive imaging members. Accordingly, in one specific embodiment of the present invention there is provided a continuous process for the fabrication of flexible seamless substrates, and flexible seamless layered photoconductive imaging members comprised of photogenerating layers and aryl amine hole transport layers by accomplishing the powder coating of a polymeric material on a mandrel, and subsequently heating the deposited polymer. Another important embodiment of the present invention relates to the preparation of flexible seamless photoconductive imaging members wherein a seamless substrate is initially prepared by the powder coating process illustrated herein, and thereafter there is deposited thereon a photogenerating layer and a hole transport layer. With the simple economical and pollution hazard free process of the present invention, there also results uniform durable and resistant substrates suitable for selection after further processing as imaging members. Additionally, pollution hazards attendant to liquid spray coating processes wherein solvents are selected are eliminated with the elastrostatic spray powder caoting process of the present invention.
Numerous different processes are known for permitting the preparation of photoconductive imaging members, including the layered imaging members as illustrated in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. In these processes, genreally a supporting substrate is provided, such as aluminized Mylar, and there is solution coated thereover a photogenerating layer comprised of, for example, trigonal selenium dispersed in an inactive resinous binder. Thereafter, a hole transport layer comprised of, for example, aryl diamine molecules dispersed in a resinous binder, is applied to the photogenerating layer by, for example, solvent coating processes. Other processes for accomplishing the preparation of layered photoresponsive imaging members include dip coating, vacuum coating, depositions with various applicators including Bird applicators, and solution spraying. In one commonly practiced prior art process, imaging members with seams therein are prepared by initially formulating the photoreceptor on a substrate such as aluminized Mylar, and subsequently cutting the resulting member into sections of the appropriate length, for example 120 centimeters long. Thereafter, the ends of each section can be ultrasonically welded providing a photoreceptor imaging belt with a seam therein.
A number of other patents are in existence describing layered photoresponsive imaging members such as, for example, U.S. Pat. No. 3,041,167 which illustrates an overcoated imaging member with a conductive substrate, a photoconductive layer, and an overcoating layer of an electrically insulating polymeric material. Layered imaging members similar to those disclosed in the present application are illustrated in U.S. Pat. Nos. 4,265,990, mentioned hereinbefore, and 4,251,612. These patents disclose photoresponsive imaging members comprised of photogenerating layers and hole transport layers, and wherein further the members obtained can be in the form of a belt with seams therein. Examples of generator layers disclosed in these patents are trigonal selenium and phthalocyanines, while examples of transport molecules that may be used include various aryl amines as mentioned therein. Other representative patents disclosing layered photoresponsive imaging members are U.S. Pat. Nos. 4,115,116; 4,047,949; and 4,081,174. These members can be prepared by a number of known methods, the process parameters and order of coating of the layers being dependent on the member desired. Thus, for example, there is described in this prior art and other U.S. patents the preparation of layered imaging members by applying to a conductive substrate containing a hoale blocking layer, a photogenerating layer utilizing solvent coating processes or laminating processes. The imaging members resulting, when provided in the form of a belt, contain seams therein; while in contrast, the imaging members produced in accordance with the process of the present invention are seamless. Imaging member belts with seams therein, while suitable for their intended purposes, have disadvantages associated therewith, including the need to sense the position of the seam to prevent it from passing through an image frame.
Additionally, there is disclosed in U.S. Pat. No. 3,671,617 methods for drawing a tubular thermal plastic resin film comprising transporting the film onto a mandrel which has a particular conical shape, causing the uniform occurrence of necking initiation points around the circumference of the film by drawing the film around the mandrel; and continuing to draw the film by the action of fluid pressure exerted within the film subsequent to the passing of the film over the main mandrel. Other similar teachings are presented in U.S. Pat. Nos. 3,576,051; 3,725,519; 4,118,453; 4,341,729 and 4,062,916.
Additional representative prior art includes U.S. Pat. No. 3,607,998 which discloses methods for obtaining hollow articles wherein a fluidized mass of material is formed, and at least a portion of the periphery of a flexible bladder is contacted with a portion of the fluidized mass in a manner that will enable the material to adhere thereto. Thereafter, the material is integrated into a cohesive unitary generally hollow article, the bladder is at least partially collapsed and is removed therefrom, reference the disclosure in column 1, lines 56 to 75. There is also disclosed in this patent that the material of the fluidized mass is in the form of integrable particles without any added substances, and most desirably the material is a thermoplastic resin, see column 1, lines 67 to 68; and column 2, lines 1 to 9. A similar teaching is present in U.S. Pat. No. 3,698,847, which is a divisional of U.S. Ser. No. 841,121 from which the U.S. Pat. No. 3,607,998, discussed herein, issued. Furthermore, in the abstract of Belgian Patent Publication No. 771,176 there is described a thermoplastic film made by electrostatic deposition of heated thermoplastic particles. Specifically, this abstract discloses a film or sheet prepared by electrostatic deposition of particles of thermoplastic materials on a moving surface, the particles being heated to a temperature sufficient to fuse them into a composite layer which is then separated from the surface prior to or subsequent to solidification of the layer by cooling. The moving surface may be an endless belt or a rotating drum of a copper alloy, stainless steel or chrome steel which is preheated. These references, however, are silent with respect to fabricating seamless substrates, and more particularly for formulating the substrate by powder spraying processes. Also of interest with respect to that aspect of the present invention relating to the removal of the seamless substrates, or seamless photoconductive members from a mandrel by, for example, introducing air through holes situated in the mandrel, are U.S. Pat. No. 1,573,386, and Japanese Patent Publication No. 201640. There is disclosed in the aforementioned documents processes for applying gas pressure from inside a mandrel and through its wall to the interface between a moulded tube or drum and the mandrel for the purpose of separating them. As indicated in column 3, line 25, of the U.S. Pat. No. 1,573,386, air is forced into the mandrel wall causing it to flow between the convolutions of the wire 12, thereby enabling tube 13 to be loosened from the mandrel whereupon it can be easily removed therefrom. Similar teachings are present in U.S. Pat. Nos. 1,036,416; 2,272,704; 2,361,026; 2,384,055; 2,604,658; 2,888,712; and 4,435,531.
Other representative prior art selected as a result of a patentability search include U.S. Pat. Nos. 3,576,928, which discloses a cylindrical member for deposition; 3,148,084, 3,439,649; 3,598,626; 3,676,210; 3,791,341; 3,849,128; 4,073,265; 4,383,020; and 4,481,273.
Although the above processes and resulting photoconductive imaging members formulated in some instances are suitable for their intended purposes, there remains a need for improved processes which are simple in operation, can be accomplished in the absence of a solvent, and which processes have the other advantantages as illustrated herein. Further, with the process of the present invention, the seamless photoresponsive imaging member can be prepared without separating the substrate from the mandrel as more fully disclosed hereinafter. Moreover, the electrostatic powder coating process of the present invention has advantages over liquid spray coating techniques. For example, in powder coating processes, organic solvents are not required, and thus the problems arising from volatile organic emissions and hazardous waste disposals are eliminated. Further, with the process of the present invention, there results extremely efficient utilization of materials in that from about 95 percent to about 99 percent of the components selected are consumed in the process. Additionally, with the process of the present invention there results extremely uniform coated layers which is not the situation with many prior art processes. Also, with the powder coating process of the present invention there may be selected insoluble and soluble polymer resins. Furthermore, with the powder coating processes of the present invention significant energy reductions are achievable, in that for example, the prefiltered exhaust air emitted from the powder booth apparatus can be recirculated for other uses. Also, it is known that powder coating technology has been used in the painting industry, reference for example a brochure available from Interrad entitled "Powder Coating: Tomorrow's Superstar in Metal Finishing" reprinted from a January 1982 issued of Modern Metals. The aforementioned prior art is silent, however, with respect to the use of powder coating processes for affecting the preparation of seamless photoresponsive imaging members.